1. Field of the Invention
This invention relates to arc extinguishing devices for electrical switchgear such as air break disconnect switches used in transmission and distribution lines.
2. Related Art
Arc extinguishing devices that include an all-metal whip element are known to the prior art for the purpose of helping minimize arcing upon switch opening.
More recently, disclosure has been made in U.S. Pat. No. 6,392,181, issued May 21, 2002, and in copending application Ser. No. 10/342,035, filed Jan. 14, 2003, by the present inventor and others, both of which are assigned to the present assignee, of arc extinguishing devices including a whip element comprising a nonmetal, such as a fiber reinforced plastic (FRP) material, with a conductive path of various forms on its surface.
All of the description of prior art all metal whips and the more recently disclosed whips including a nonmetal of the above-mentioned patent and copending application is incorporated herein by reference.
In the materials art, there is a class of materials referred to as metal matrix composites (or MMCs) that have been long known and have been applied to and/or are of interest for structures in automotive and other applications. Such composite materials and prior known intended uses are described, for example, in an article by Hunt et al., xe2x80x9cAutomotive Applications of Metal-Matrix Compositesxe2x80x9d, pp. 1029-1032; and an article by Sain, xe2x80x9cEngineering Compositesxe2x80x9d, pp. 1-20, at www.unb.calweb/pandp centre/engcomp/engcomp.htm.
The present invention is directed to arc extinguishing devices with a whip that comprises (at least a tip portion that flexes in contact with a latch of the device and is last to separate and spring away from the latch) a metal matrix composite (MMC), which is a term embracing composite members of a metal matrix containing reinforcing fibers, such as, but not limited to, alumina fiber reinforced aluminum (sometimes referred to as FRA) as described in the aforementioned publications, which are incorporated by reference herein for their description of practices with such materials.
Other features and characteristics of arc extinguishing devices of the present invention may, singly or in various combinations, be in accordance with or similar to those of the above copending application including, for example, the combination in a whip of an MMC rod with an all-metal base rod that is first to engage the latch of the device upon switch opening and switch closing; an MMC rod that is a tapered tube and, in a further embodiment, has another MMC rod disposed within it; and having a wheel on the latch with which the MMC rod makes sliding conductive contact during switch opening.
The invention offers alternatives to whips that are all uniform metal throughout (referred to as xe2x80x9call-metalxe2x80x9d) and also to whips that comprise fiber reinforced plastic. MMC materials have high specific strength (strength in relation to density). While some known MMC materials are characterized by high hoop strength, because that is favorable for the structures previously intended, the strength can be subject to the orientation of the reinforcing fibers, e.g., by having the fibers run lengthwise through an MMC whip rod, rather than laterally or circumferentially, greater bending strength can result. Further, an MMC whip element does not necessitate a conductor to be applied to it for adequate conduction over the entire whip length, as is generally the case with FRP whips. However, an MMC whip may have a further conductor on it if desired for any propose purpose, such as a brazing alloy, if one is used to consolidate MMC sheets or tapes into a desired rod configuration, or a more durable metal part to enhance arc resistance.
Consequently, embodiments of the invention are believed attractive in facilitating achievement of high speed separation for rapid arc extinguishing, relative to all-metal whips, and avoiding the need for an applied conductor for sliding engagement with a latch as generally is needed with FRP whips. Regardless of the reasons for adopting the inventive apparatus, it provides the art with further alternatives not previously known.